Playlist issues between WMP (Win 10) and Groove (Win 10 Mobile)

I've been a fan of Windows mobile for many years and have just updated to a Lumia 950XL. Liking it very much so far, but find irritating the lack of a decent offline player with real playlist support. Groove is driving me nuts!

I have a well connected home, and use a couple of network music players (Pure Sensia & MusicPal) to stream music via Serviio and a local PC that acts like a server. When I updated to Windows 10 on my PC's I discovered that Windows 10 would not connect to any shared folders on the LAN if I used a Microsoft account, thus I've had to use all local accounts on my home PC's. This is a real irritation that I wish Microsoft would fix, but that's another issue

As all my music is on this "Server" and was organised with playlists and tags already, I was not interested in recreating all this manually on my phone. Basically I wished to copy selected playlists to my phone SD card so that they were available when I fly, or travel.

Using WMP I opened the playlists, and synced them to the phone SD card without any issue. Unfortunately the playlists themselves were not created on the phone. I tried to open the files I'd copied directly from WMP and then save the playlist back to the phone, but WMP would open these, but not let me save the playlist back.

Now becoming rather irritated that two Microsoft products refuse to talk sensibly to each other. Reluctantly I reinstall groove on my PC, and point it at my shared music library. Then discover that Groove does not work with any networked location!

Uninstall this piece of dross and start hunting for solutions online and discover I've run into a real can of worms...

Can anyone here help? I'm stumped at the moment, and would really appreciate guidance from the guru's present.

I won't/can't defend Groove when it comes to syncing or sharing playlists. Not my favorite part of Groove. Not even having wireless sync is amazingly annoying. Makes me miss WP7 and Zune. However, I found some ways which makes it easier to manage.

PCs
I use OneDrive for this -- not playing from OneDrive, but using it to sync "locally" to multiple devices.

1. Put all your music on OneDrive Music folder.
2. Set each PC to sync OneDrive (both ways). Thus each PC gets a OneDrive\Music folder.
3. Reset your PCs must library to include only the OneDrive\Music folder.
4. Ensure PC Groove is set to point only to the OneDrive\Music folder.
5. Ensure PC Groove apps are set to only show songs available offline (i.e. don't let them stream from Groove).

For multiple PCs... this is easy. Your music is always on OneDrive. You could stream it if you needed to. Anytime you, add, etc. music on one PC, within a couple of minutes it is on another. You can setup your media PC to share music or setup Plex for non-PC devices, etc. Playlists (or the PCs) are also fine. Purchasing or re-downloading is also fine. Everyone gets it and Groove knows that it is already there.

WP 10 Syncing
No real easy way to do this. If anyone else knows... I'd love to hear it. For me...

I put a large SD card in my phone, such that it can hold my entire library. Partial sync'ing I found not to be worth it. I just plug in my phone, use Explorer, look at the OneDrive\Music directory and sort by date descending. Same with the Phone\SD\Music directory. I can quickly see which aren't on the phone and just copy them over.